Guaiane Sesquiterpene Lactones and Amino Acid-Sesquiterpene Lactone Conjugates from the Aerial Parts of Saussurea pulchella

Two new guaiane sesquiterpene lactones (1 and 2) and seven new amino acid-sesquiterpene lactone conjugates (3−9), together with six known sesquiterpene lactones (10−15), were isolated from the methanol extract of the aerial parts of Saussurea pulchella. Their structures were determined on the basis of spectroscopic and chemical methods to be 8α-O-(3′-hydroxy-3′-methylbutyryl)desacylcynaropicrin (1), 8α-O-(2′, 3′-dihydroxyisobutyryl)11β,13-dihydrodesacylcynaropicrin (2), and pulchellamines A, B, C, D, E, F, and G (3−9). The structures of the new amino acid-sesquiterpene lactone conjugates, pulchellamines A, B, C, D, E, F, and G (3−9), were confirmed by synthesis. The isolated compounds were evaluated for cytotoxic activity against four human tumor cell lines. Compounds 11 and 12 exhibited cytotoxicity against skin melanoma (SK-MEL-2) and ovary malignant ascites (SK-OV-3) human tumor cell lines with ED50 values of 1.53 and 4.07 µM, and 2.49 and 7.42 µM, respectively.